Method for packaging no/n2 mixtures, with prior purging and rinsing steps

ABSTRACT

The method for packaging a gaseous NO/N 2  mixture into at least one container, characterized in that, prior to admitting the said NO/N 2  mixture, said at least one container is subjected to at least a purging step during which the internal volume of the container is placed in fluidic communication with the ambient atmosphere, an evacuating step during which the internal volume of the container is placed under depression, and a gas rinsing step during which an inert gas is admitted to said at least one container. For preference, the final gaseous NO/N 2  mixture contains an NO content less than or equal to 1200 ppm by volume for a pressure of between P1 and 800 bar.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of priority under 35 U.S.C. §119 (a)and (b) to French Application No. 1155038 filed Jun. 9, 2011, the entirecontents of which are incorporated herein by reference.

BACKGROUND

The invention relates to a method for packaging a gaseous NO/N₂ mixtureinto a container, particularly one or more gas cylinders, comprisingvarious successive purging and gas rinsing steps.

Gaseous NO/N₂ mixtures are commonly used to treat pulmonaryvasoconstrictions in adults or children, particularly in new borninfants suffering from primary pulmonary hypertension or in patients whohave undergone cardiac surgery.

These NO/N₂ mixtures are conventionally packaged into steel gascylinders. Typically these cylinders contain, by volume, from 100 to1000 ppm of NO, the remainder being nitrogen (N₂). These cylindersusually have a water capacity of 2 to 50 litres, which means that atotal charge of as much as 15 m³ of NO/N₂ mixture can be admitted tothem.

The packaging of these mixtures, which means the filling of cylinderswith these mixtures, is done at gas filling centres.

However, given the low NO content in the mixture, which is typically ofthe order of a few hundred ppm by volume, it is not always easy topackage these mixtures on an industrial scale. In particular, thegaseous NO/N₂ mixture is sensitive to the presence of residualimpurities of the oxygen type likely to be present in the cylinders atthe time of their filling.

Indeed it is of the utmost importance to be able to ensure that thecylinders, prior to being filled, have been correctly rid of all thegaseous impurities they are likely to contain, particularly oxygen whichcan react with the NO to form toxic NO₂.

Stated differently, if the internal volume of the cylinders is notcorrectly purged and cleaned, the NO/N₂ mixtures produced will notcomply with the specifications and will have to be scrapped.

The problem is therefore that of providing an improved packaging methodthat makes it possible to eliminate all or almost all of the impurities,especially oxygen, likely to be found in one or more gas cylinders thatare to receive a gaseous mixture of the NO/N₂ type.

SUMMARY

The solution of the invention is therefore a method for packaging agaseous NO/N₂ mixture into at least one container, in particular one ormore gas cylinders, characterized in that, prior to admitting said NO/N₂mixture, said at least one container, which means to say the containeror containers, is subjected to at least:

-   -   a) a purging step during which the internal volume of the        container is placed in fluidic communication with the ambient        atmosphere,    -   b) an evacuating step during which the internal volume of the        container is placed under depression, which means to say that        the internal pressure of the container is reduced until it        reaches a pressure lower than atmospheric pressure (<1 bar        absolute), and    -   c) a gas rinsing step during which an inert gas is admitted to        said at least one container.

Depending on circumstance the method of the invention may have one ormore of the following technical features:

-   -   Evacuating step b) is performed by withdrawing gas using a        vacuum pump.    -   Said at least one container is subjected to steps a) and c)        several times in succession prior to said NO/N₂ mixture being        admitted into the said at least one container.    -   Two successive sequences of steps a) and c) are separated by a        sequence of steps a), b) and c).    -   A sequence of steps a), b) and c) is immediately followed by a        sequence of steps a) and c) or by a sequence of steps a), c) and        a).    -   During steps c), the inert gas used to perform the gas rinsing        is nitrogen.    -   Several gas containers are subjected simultaneously to steps a)        to c).    -   After at least two sequences of steps a) and c) have been        carried out, a gaseous mixture made of NO and N₂ is admitted to        the container or containers.    -   After at least two sequences of steps a) and c) have been        carried out, the following are admitted in succession to the        container or containers:        -   i) a gaseous premix made of NO and N₂ containing an NO            content less than 10% by volume until a first pressure P1 is            reached where P1>1 bar absolute;        -   ii) gaseous nitrogen until, through mixing of the nitrogen            with the said NO/N₂ premix, a final gaseous NO/N₂ mixture            containing an NO content less than or equal to 1200 ppm by            volume and a second pressure P2 of between P1 and 800 bar            are achieved.    -   Gas rinsing step c) involves admitting gaseous nitrogen into the        container or containers until a rinsing pressure of between 2        and 20 bar, preferably of between 2 and 12 bar, is reached        within said container or containers.    -   During the purging step a), the internal volume of the container        is kept in fluidic communication with the atmosphere as long as        the internal pressure inside the container is higher than a        minimal purge pressure (Pmin) such that 3.5 bar>Pmin>1 bar,        preferably between around 1.1 and 3 bar.    -   During at least one evacuating step b), the internal volume of        the container is placed under depression until a pressure level        below 0.5 bar, preferably below 0.2 bar is reached.    -   It comprises, prior to step a), a step d) of evacuating and a        step e) of purging at least one flexible hose connecting the        filling system to a gas container.    -   During the gas rinsing step c), the admission of inert gas to        the said at least one container is halted when the pressure in        said at least one container reaches a value of between 2 and 20        bar, preferably of between 3 and 10 bar.    -   Fluidic communication with the ambient atmosphere during purging        step a) is halted when the pressure in the internal volume of        the container reaches a value of between 1 and 1.5 bar.    -   The first pressure P1 is between 2 and 10 bar, preferably less        than or equal to 5 bar.    -   The second pressure is between 100 and 700 bar, preferably at        least 200 bar.    -   The gaseous premix made of NO and N₂ contains an NO content less        than or equal to 8% by volume, preferably an NO content less        than or equal to 5% by volume.    -   The gaseous premix made up of NO and N₂ contains an NO content        of the order of 4% by volume and the first pressure P1 is of the        order of 2 to 10 bar abs, for example of the order of 2 to 5 bar        abs.    -   The final gaseous NO/N₂ mixture contains an NO content less than        or equal to 1000 ppm by volume, preferably the final gaseous        NO/N₂ mixture contains an NO content of between 200 and 1000 ppm        by volume and more preferably still, of between 200 and 800 ppm        by volume.    -   It is performed using a gas container filling system comprising        means of connection allowing several containers to be filled at        once.    -   The container is a gas cylinder, preferably a gas cylinder with        a body made of steel, of aluminium or an aluminium alloy.    -   In the context of the present invention, the pressures quoted        are absolute pressures.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be better understood by virtue of the descriptiongiven hereinafter with reference to the attached figures in which:

FIG. 1 schematically illustrates one embodiment of a packaging cycleaccording to the present invention, and

FIG. 2 is the diagram of an installation for implementing the method ofthe invention.

FIG. 1 schematically depicts one embodiment of a packaging cycle thatcan be applied in the context of the method of packaging the gaseousNO/N₂ mixture of the present invention.

DESCRIPTION OF PREFERRED EMBODIMENTS

As can be seen, this packaging cycle comprises several successive steps,spaced out over time from T0 to T13, and which are applied to eachcylinder and are detailed hereinbelow. Successive steps a) to c) of themethod of the invention have been indicated in FIG. 1.

Between T0 and T1, the flexible hoses of the installation are vented tothe open air, which means to say that the internal volume of theflexible filling hoses is placed in fluidic communication with theambient atmosphere in order to remove any possible residual raisedpressure. During this phase, the valve or valves of the gas containersconnected to the hoses are closed, so that there is no exchange of gaswith the container or containers. This corresponds to step d) of themethod.

Between T1 and T2, a vacuum pump is used to place the inside of theflexible hoses under connected depression, i.e. under a pressure belowatmospheric pressure, for example of the order of 0.15 bar, thus makingit possible to remove any residual gas and/or air contained therein.This phase is therefore also performed with the cylinder valve closed.Placing the flexible hoses under vacuum is a safety measure which makesit possible to check that all the hoses are correctly connected and thatthere are no leaks. Specifically, if there was a leak or if a hose wasincorrectly connected, it would not be possible to establish the stablevacuum. This corresponds to step e) of the method schematicallyillustrated in FIG. 1.

Between T2 and T3, the operator opens the valve on each cylinder and theresidual pressure present in each cylinder then rises and reaches thepressure sensor, which detects the said rise in pressure. Typically theresidual pressure in the cylinder is of the order of around 3 to 4 barabsolute. Before T2, no gas rinsing of the container with nitrogen tookplace. This corresponds to step f) of the method schematicallyillustrated in FIG. 1.

Between T3 and T4, the actual treatment of each cylinder begins. Morespecifically, each cylinder is vented to the atmosphere, i.e. the gascontained in the cylinder is allowed to escape to the externalatmosphere under the simple effect of the difference in pressure betweenthe inside and the outside of the cylinder, so as to decrease theinternal pressure of the cylinder to atmospheric pressure. Thiscorresponds to step a) of the method of the invention. At T4, theinternal pressure of the gas cylinder is therefore more or less equal toatmospheric pressure (1 atm=around 1 bar absolute), i.e. of the order of1 to 1.5 bar abs.

Between T4 and T5, the cylinder is rinsed with nitrogen while itsinternal pressure is raised to around 10 bar. The addition of nitrogenis performed via a gas line and/or a store of nitrogen under pressure soas to raise the internal pressure of the cylinder to the desiredpressure. This corresponds to step c) of the method of the invention.

Between T5 and T6, the nitrogen contained in the cylinder is againallowed to escape to the atmosphere, which allows any impurities thatmight be present in the cylinder to be removed. This corresponds to afurther step a) of the method of the invention.

Between T6 and T7, the cylinder is purged by placing its internal volumeunder depression by withdrawing the residual gas contained therein usinga vacuum pump until an internal depression of below 0.2 bar abs,preferably of below 0.1 bar, for example of the order of 0.05 bar, isreached. This corresponds to a further step b) of the method of theinvention.

Between T7 and T8, the cylinder undergoes a further rinsing withnitrogen to raise its internal pressure to around 10 bar as between T4and T5. This corresponds to a further step c) of the method of theinvention.

Between T8 and T9, the cylinder is once again discharged to the ambientatmosphere as during times T5 and T6. The residual gas pressure is thenkept at around 1.35 bar in order to avoid unwanted ingress ofatmospheric contaminants. This corresponds to a further step a) of themethod of the invention.

Between T9 and T10, the cylinder once again undergoes additional rinsingwith nitrogen to raise its internal pressure to around 10 bar, asbefore. This corresponds to a further step c) of the method of theinvention.

Between T10 and T11, the nitrogen is discharged into the atmosphere, asbetween T8 and T9 and between T5 and T6, but this time maintaining aresidual internal pressure of the order of 3 bar. This corresponds to afurther step a) of the method of the invention.

Between T11 and T12, a gaseous premix formed of NO and N₂ containing anNO content less than 10% by volume is admitted to the cylinder in orderto reach a first filling pressure P1 where P1>1 bar, typically apressure P1 of the order of 2 to 10 bar abs, preferably of around 3 to 5bar abs. Advantageously, the gaseous premix formed of NO and N₂ containsan NO content of the order of 4% by volume.

Between T12 and T13, gaseous nitrogen is then admitted to the containercontaining the NO/N₂ premix at the first pressure P1 in order to obtaina final gaseous NO/N₂ mixture containing an NO content less than orequal to 1200 ppm by volume, for example a final NO content of 200 to800 ppm, and a second pressure P2 of between P1 and 800 bar, for examplein this instance a pressure of 180 to 200 bar.

This method can be implemented via a packaging installation like the onedepicted schematically in FIG. 2, fitted with a filling system 14 forfilling gas containers, i.e. gas cylinders, comprising connecting means15 allowing several containers 11 to 13 to be connected at once,typically that allow simultaneous connection of 2 to 20 cylinders.

The nitrogen is stored in the reservoir 1 in liquid form and thenwithdrawn in liquid form by a cryogenic pump 2 which compresses it to apressure of the order of 100 to 300 bar, before sending it to anatmospheric heater 3 where it is vaporized to yield gaseous nitrogen. Asmay be seen, it comprises a main line or pipe 20 for carrying nitrogenfrom a reservoir 1 to the filling system 14. In fact, the pressure inthe line varies between around 100 bar immediately downstream of theoutflow from the buffer volume into the cylinders and around 260 barwhich corresponds to the threshold at which the pump is stopped.

The nitrogen gas is then carried by the line 20 to a purification device6 able to eliminate traces of O₂ and H₂O, for example using a suitablemolecular sieve, for example of the zeolite, silica gel, alumina orsimilar type, or mixtures thereof.

It should be noted that the line 20 is also fluidically connected to abuffer volume 4 capable of storing some of the gaseous nitrogen, and tobackup racks 5, each comprising several nitrogen cylinders.

Moreover, the installation also comprises a cabinet 16 comprisingseveral cylinders 9 of an NO/N₂ premix, here containing 4% by volume ofNO, which cylinders 9 are fluidically connected to the line 20 by anNO/N₂ premix supply line 22. In fact, the NO/N₂ line 22 and the nitrogenline 20 are not connected directly to one another but are connected tothe valve unit 8 which is itself connected by the line 21 to the fillingsystem or systems 14. The valves in the valve unit 8 make it possible toselect the fluid with which the cylinders 11 to 13 of the system 14 arefilled. The nitrogen line 20 and the NO/N₂ premix line 22 are thereforefluidically connected firstly by the valve unit 8 then a common section21 to the filling system 14. The valve unit 8 comprises valves, controlelements controlled by the control device 10, etc.

Flow meters 7 make it possible to measure the quantity of N₂ and NOflowing through the lines 20 and 22 and to transmit the measuredinformation to a control device 10, such as a computer or the like. Theinstallation also comprises a vent-to-atmosphere line 17 allowing thegases to be discharged to the ambient atmosphere, notably during thepurge step or steps during which the internal volume of the container isplaced in fluidic communication with the ambient atmosphere.

A vacuum pump (not shown) allows the container or containers to beevacuated, i.e. allows their internal pressure to be reduced down to apressure below atmospheric pressure, i.e. <1 bar absolute.

It will be understood that many additional changes in the details,materials, steps and arrangement of parts, which have been hereindescribed in order to explain the nature of the invention, may be madeby those skilled in the art within the principle and scope of theinvention as expressed in the appended claims. Thus, the presentinvention is not intended to be limited to the specific embodiments inthe examples given above.

1. A method for packaging a gaseous NO/N₂ mixture into at least onecontainer, wherein, prior to admitting said NO/N₂ mixture into thecontainer, said at least one container is subjected to at least: a) apurging step during which the internal volume of the container is placedin fluidic communication with the ambient atmosphere, b) an evacuatingstep during which the internal volume of the container is placed underdepressurization, and c) a gas rinsing step during which an inert gas isadmitted to said at least one container.
 2. The method of claim 1,wherein said at least one container is subjected to steps a) and c)several times in succession prior to said NO/N₂ mixture being admittedto said at least one container.
 3. The method of claim 1, wherein atleast two successive sequences of steps a) and c) are separated by asequence of steps a), b) and c).
 4. The method of claim 1, wherein asequence of steps a), b) and c) is immediately followed by a sequence ofsteps a) and c) or by a sequence of steps a), c) and a).
 5. The methodof claim 1, wherein, during steps c), the inert gas used to perform thegas rinsing is nitrogen.
 6. The method of claim 1, wherein several gascontainers are subjected simultaneously to steps a) to c).
 7. The methodof claim 1, wherein, after at least two sequences of steps a) and c)have been carried out, a gaseous mixture made of NO and N₂ is admittedto the container or containers.
 8. The method of claim 1, wherein, afterat least two sequences of steps a) and c) have been carried out, thefollowing are admitted in succession to the container or containers: i)a gaseous premix made of NO and N₂ containing an NO content less than10% by volume until a first pressure P1 is reached where P1>1 barabsolute; ii) gaseous nitrogen until, through mixing of the nitrogenwith the said NO/N₂ premix, a final gaseous NO/N₂ mixture containing anNO content less than or equal to 1200 ppm by volume and a secondpressure P2 of between P1 and 800 bar are achieved.
 9. The method claim1, wherein the gas rinsing step c) involves admitting gaseous nitrogeninto the container or containers until a rinsing pressure of between 2and 20 bar, preferably of between 2 and 12 bar, is reached within saidcontainer or containers.
 10. The method of claim 1, wherein during thepurging step a), the internal volume of the container is kept in fluidiccommunication with the atmosphere as long as the internal pressureinside the container is higher than a minimal purge pressure (Pmin) suchthat 3.5 bar>Pmin>1 bar.
 11. The method of claim 10, wherein Pmin isbetween about 1.1 and about 3 bar.
 12. The method of claim 1, whereinduring at least one evacuating step b), the internal volume of thecontainer is placed under depressurization until a pressure level below0.5 bar is reached.
 13. The method of claim 12, wherein thedepressurization pressure level is below 0.2 bar
 14. The method of claim1, wherein it comprises, prior to step a), a step d) of evacuating and astep e) of purging at least one flexible hose connecting the fillingsystem to a gas container.
 15. The method of claim 1, wherein the finalgaseous NO/N₂ mixture contains an NO content less than or equal to 1000ppm by volume.
 16. The method of claim 15, wherein the final gaseousNO/N₂ mixture contains an NO content of between 200 and 800 ppm byvolume.
 17. The method of claim 1, wherein during the gas rinsing stepc), the admission of inert gas to said at least one container is haltedwhen the pressure in said at least one container reaches a value ofbetween 2 and 20 bar.
 18. The method of claim 17, wherein the value isbetween 3 and 10 bar.
 19. The method of claim 1, wherein fluidiccommunication with the ambient atmosphere during purging step a) ishalted when the pressure in the internal volume of the container reachesa value of between 1 and 1.5 bar.